Big problem with TextField formating

i have TextField with this properties:

description_txt.width = 270;
description_txt.multiline = true;
description_txt.wordWrap = true;
description_txt.text = _descriptionText;
description_txt.height = 400;

then i try to align scrollbar arrows next to the description_txt field.

upArrow.y = description_txt.y;
downArrow.y = description_txt.y+description_txt.height;

i use scrollV += 1; method for scrolling text…
my problem is how to get the y of the last visible line of text (bottomScrollV) and then align downArrow to it. Or maybe another solution, how to format textField that it’s bottom border jumps just beneth last visible text line, then i’ll just allign arrow to this position.

i use this method for scroling couse i dont like scroling TextField in the Sprite, sometimes it just cuts type on the last line and that looks ugly…

here is the picture of that situation
http://vedran.webfactional.com/kontenjner/Picture%204.png

thnx!